4 INTRODUCTION 
kinds of plants according to some system (whence the 
term, systematic). 
(b) Taxonomy, or the principles of classification, based 
upon the facts observed and their interpretation. 
(c) Nomenclature, the principles and rules adopted for 
the formation and assignment of plant names. 
6. Morphology. If, in our study, our attention is 
centered chiefly on structure and form, our point of view 
is that of morphology, and we recognize external and 
internal anatomy, microscopic anatomy (histology), com- 
parative morphology, experimental morphology (which 
attempts to ascertain, by experiment; the causes of form 
and structure), embryology (the study of embryos), and 
other subdivisions. 
7. Physiology. If we are interested primarily in what 
the various parts of the plant are doing, rather than in their 
form and structure, our point of view is that of physiology. 
We shall find, as we study, that the facts of form cannot 
be understood or explained except in the light of the 
physiological work of the given part; and conversely, 
that physiological work cannot be explained unless the 
structure is also understood. 
8. Ecology. Every plant lives in a certain place, with 
certain external surroundings; in other words it has a 
home, or, as we usually say, a habitat or environment. 
In order to live and keep healthy the plant must be 
favorably adjusted to the various features (factors) of its 
environment the range of temperature, amount of light 
and moisture, components of the soil, the earth's at- 
traction (gravity), and surrounding animals and other 
plants. The science of the relation of living things to their 
environment is Ecology. 
